Method for fabrication of ceramic dielectric films on copper foils

ABSTRACT

The present invention provides a method for fabricating a ceramic film on a copper foil. The method comprises applying a layer of a sol-gel composition onto a copper foil. The sol-gel composition comprises a precursor of a ceramic material suspended in 2-methoxyethanol. The layer of sol-gel is then dried at a temperature up to about 250° C. The dried layer is then pyrolyzed at a temperature in the range of about 300 to about 450° C. to form a ceramic film from the ceramic precursor. The ceramic film is then crystallized at a temperature in the range of about 600 to about 750° C. The drying, pyrolyzing and crystallizing are performed under a flowing stream of an inert gas. In some embodiments an additional layer of the sol-gel composition is applied onto the ceramic film and the drying, pyrolyzing and crystallizing steps are repeated for the additional layer to build up a thicker ceramic layer on the copper foil. The process can be repeated one or more times if desired.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/183,148, filed on Jun. 2, 2009, which is incorporated herein byreference in its entirety.

CONTRACTUAL ORIGIN OF THE INVENTION

The United States Government has rights in this invention pursuant toContract No. W-31-109-ENG-38 between the United States Government andThe University of Chicago and/or pursuant to Contract No.DE-AC02-06CH11357 between the United States Government and UChicagoArgonne, LLC representing Argonne National Laboratory.

FIELD OF THE INVENTION

This invention relates to preparation of ceramic dielectric films. Moreparticularly, the invention relates to methods for preparation ofceramic dielectric films on copper foils.

BACKGROUND OF THE INVENTION

The development of power electronic devices with improved performance,increased reliability, compact size, and reduced weight requires thepassive components to be embedded within a printed wire board (PWB).This technology could free up surface space, increase devicereliability, and minimize electromagnetic interference and inductanceloss. The capacitance density of a dielectric is proportional to itspermittivity or dielectric constant divided by the thickness of thedielectric material. A high capacitance density capacitor can befabricated by using thin film dielectric of high permittivity. Highpermittivity (high-K) materials include perovskite ceramics of generalformula ABO₃, such as crystalline lead zirconate titanate [Pb(Zr,Ti)O₃,PZT], lead lanthanum zirconate titanate [(Pb,La)(Zr,Ti)O₃, PLZT], leadmagnesium niobate [Pb(Mg_(1/3)Nb_(2/3))O₃, PMN], barium titanate(BaTiO₃, BT), and barium strontium titanate [(Ba,Sr)TiO₃, BST]. Thinceramic films may be deposited on base metal foils, such as nickel andcopper. Base metal foils are subject to undesirable oxidation andrequire low oxygen partial pressures during high temperature annealingfor formation of the desired crystalline phase of the ceramic thatexhibits high-K. The low oxygen partial pressures, however, can resultin complications such as high dielectric losses due to reduction ofdielectric materials, suppression of dielectric constant due toreactions between the thin film dielectrics and the substrates of metalfoils. Therefore, finding an effective method for the fabrication ofhigh-K dielectric films on metal foils has been a hot research area[1-3]. Zou et al. [1] describe a method of using LaNiO₃ (LNO) buffer ona nickel substrate to prevent oxidation at the interface and thereforeenable high temperature annealing processes in air. Copper is apreferred substrate due to its ready availability and PWB processingcompatibility. Borland et al. [2] describe a method of producing BSTfilms on Cu substrates by chemical solution deposition; and indicatethat a suitable oxygen partial pressure of about 10⁻¹⁰ atm must bemaintained during the high temperature annealing. Maria et al. [3]describe a method of controlling the oxygen partial pressure during hightemperature annealing by using gas mixtures between CO and CO₂ or H₂ andH₂O, in which the thermodynamic properties of the oxygen-containingsubstance are used to achieve the desired oxygen partial pressure (pO₂)during the high temperature annealing.

Recently, (Pb,La)(Zr,Ti)O₃ (PLZT) and Pb(Zr,Ti)O₃ (PZT) based perovskitematerials deposited directly on copper metal foils have been of greatinterest because of reduced manufacturing costs achievable by replacingexpensive noble metal electrodes in embedded capacitor applications.Traditionally, lead-based perovskite materials have been deposited onexpensive Pt/Si substrates by sol-gel synthesis and crystallized at hightemperatures in air. The in-air processing capability cannot be extendedto perovskites deposited onto copper substrates, because the ease withwhich copper forms a copper oxide (Cu₂O) layer under such processingconditions. The low-permittivity and linear dielectric Cu₂O layerdegrades the ferroelectric properties of the resultant capacitorstructures. Kingon et al. [4] reported that a strict control of theoxygen partial pressure (pO₂) within the thermodynamic processing window(pO₂ of about 10⁻¹³−10⁻¹⁷ atm) during crystallization is necessary toavoid the formation of copper oxide, while maintaining the high qualityand phase integrity of the perovskite material. Losego et al. [5]indicate that careful choice of solution chemistry is important to avoidcopper oxidation and micro-cracking in films made directly on coppersubstrates. While acetic acid [4-7], alkanolamine [6], and acetylacetone[6], based chelation methods have been used in the literature to depositfilms on copper, 2-methoxyethanol (2-MOE)-based chemistry has beenreported to promote the desired reactions and can solubilize a varietyof different precursors [8].

SUMMARY OF THE INVENTION

The present invention provides a method for the fabrication of PLZTceramic thin film directly on bare copper substrate to form highcapacitance density dielectric sheets for embedding in PWB. The methodemploys a simple inert gas atmosphere, and does not require a bufferlayer with foreign substance (other than the dielectric material usedfor thin film coating) or a specialized gas mixture for controlling theoxygen partial pressure during high temperature annealing.

The method of the present invention comprises applying a layer of asol-gel composition onto a copper substrate (e.g., a copper foil). Thesol-gel composition comprises a precursor of a ceramic materialsuspended in 2-methoxyethanol. Typically, the precursor comprises one ormore metal salts (e.g., metal carboxylates, metal nitrates, and thelike) and/or metal alkoxide materials (e.g., metal isopropoxides ormetal propoxides). The layer of sol-gel is then dried at a temperatureup to about 250° C. The dried layer is then pyrolyzed at a temperaturein the range of about 300 to about 450° C. to form an amorphous filmfrom the chemical precursor solution. Optionally, one or two additionallayers of the sol-gel composition can be applied onto the ceramic film,repeating the drying and pyrolysis steps for each additional layer, tobuild up a thicker ceramic film on the copper substrate. The ceramicfilm is then crystallized at a temperature in the range of about 600 toabout 750° C. The pyrolyzing and crystallizing are performed under aflowing stream of an inert gas (e.g., purified nitrogen) to inhibitcopper oxidation. In some embodiments one or more additional layers ofthe sol-gel composition are applied onto the crystallized ceramic film,and the other steps or the process are repeated for each additionallayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows XRD patterns of 1-, 3- and 6-layer PLZT thin films oncopper substrates indicating the lack of substrate oxidation. A plainpolished copper substrate processed along with the films shows theformation of Cu₂O. Inset shows a typical SEM micrograph of PLZT films oncopper crystallized at 650° C.

FIG. 2 shows P-E hysteresis loops of 3-layer (345 nm) films crystallizedat various temperatures. Inset shows the change in the coercive field(2E_(c)) of the films with crystallization temperature. The top curve,in grey, provides data for films crystallized at 700° C., the middlecurve provides data for films crystallized at 675° C., and the bottomcurve provides data for films crystallized at 650° C.

FIG. 3 shows leakage current density as a function of time for 3-layer(345 nm) films crystallized at various temperatures. Inset shows thechange in leakage current density (at 1000 seconds) with crystallizationtemperature.

FIG. 4 shows room temperature dielectric response as a function of biasfield for 6-layer (690 nm) films crystallized at 650° C. Inset shows theexperimental change in the capacitance (Temperature coefficient ofcapacitance, TCC in %) as a function of temperature of the filmscrystallized at 650° C. Dotted line indicates extrapolated values.Shaded region represents the tolerance limits of commercially availableX8R capacitors.

FIG. 5 shows a graph of relaxation current density as a function of timefor PLZT/Cu at room temperature.

FIG. 6 provides a graph of relative permittivity and dielectric loss asa function of temperature for a PLZT/Cu capacitor.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention provides a method for fabricating a ceramic filmon a copper foil. The method comprises the steps of: (a) applying onto acopper substrate a layer of a sol-gel composition comprising a precursorof a ceramic material suspended in 2-methoxyethanol; (b) drying thelayer of step (a) at a temperature up to about 250° C.; (c) pyrolyzingthe dried layer from step (b) at a temperature in the range of about 300to about 450° C. (e.g., at about 450° C.) to form a ceramic film fromthe ceramic precursor; (d) optionally applying one or two additionallayers of the sol-gel composition onto the ceramic film from step (c)and repeating steps (b), and (c) for each additional layer, to build upa thicker ceramic film on the copper substrate; (e) crystallizing theceramic film from step (c) at a temperature in the range of about 600 toabout 750° C.; and (f) optionally applying one or more additional layersof the sol-gel composition onto the crystallized ceramic film from step(e), and repeating (b), (c), (d), and (e) for each additional layer. Thepyrolyzing and crystallizing steps are performed under a flowing streamof inert gas to maintain a suitably low oxygen level. Preferably, thelayers of sol-gel composition are applied by spin coating.

Any ceramic material that can be prepared by pyrolysis of a sol-gelcomposition can be prepared by the methods of the present invention.Non-limiting examples of such ceramic materials include perovskiteceramics of general formula ABO₃, such as crystalline lead zirconatetitanate [Pb(Zr,Ti)O₃, PZT], lead lanthanum zirconate titanate[(Pb,La)(Zr,Ti)O₃, PLZT], lead magnesium niobate[Pb(Mg_(1/3)Nb_(2/3))O₃, PMN], barium titanate (BaTiO₃, BT), and bariumstrontium titanate [(Ba,Sr)TiO₃, BST]. In some preferred embodiments,the ceramic material is a PLZT material and the ceramic precursorcomprises a lead compound (e.g., a lead salt such as lead acetate), alanthanum compound (e.g., a lanthanium salt such as lanthanum nitrate),a zirconium compound (e.g., a zirconium alkoxide such as zirconiumpropoxide), and a titanium compound (e.g., a titanium alkoxide such astitanium isopropoxide). As used herein, the term “copper substrate”encompasses any copper-containing metallic substance. Preferably, thecopper substrate comprises a copper foil, e.g., a metallic foilcomprising mainly copper, preferably at least about 90% copper, morepreferably at least about 95% copper (e.g., 97%, 98% 99%, or greater).Preferably, the copper foil has a thickness in the range of about 0.01to about 1 mm. Preferably the copper substrate has a polished surfacewith RMS surface roughness of not more than approximately 10 nm.

Any inert gas capable of maintaining a pO₂ of less than about 10⁻⁶ atmcan be utilized in the methods of the present invention. One preferredinert gas is a purified nitrogen capable of maintaining a pO₂ of lessthan about 10⁻⁶ atm.

In a preferred embodiment, the method is performed with the optionalstep (d), and preferably with optional step (f), to build up a thickerceramic layer on the copper substrate.

A preferred method for fabricating a PLZT ceramic film on a coppersubstrate of the present invention comprises the steps of (a) applyingonto the copper substrate a layer of a sol-gel composition containing aceramic precursor comprising a lead compound, a lanthanum compound, azirconium compound, and a titanium compound in 2-methoxyethanol; (b)drying the layer of step (a) at a temperature up to about 250° C.; (c)pyrolyzing the dried layer from step (b) at a temperature in the rangeof about 300 to about 450° C. (e.g., about 450° C.) to form a PLZTceramic film from the ceramic precursor; (d) optionally applying one ortwo additional layers of the sol-gel composition onto the ceramic filmfrom step (c) and repeating steps (b), and (c) for each additionallayer, to build up a thicker ceramic film on the copper substrate; (e)crystallizing the ceramic film from step (c) at a temperature in therange of about 600 to about 750° C.; and (f) optionally applying one ormore additional layers of the sol-gel composition onto the crystallizedceramic film from step (e), and repeating (b), (c), (d), and (e) foreach additional layer. The pyrolyzing and crystallizing steps areperformed under a flowing stream of inert gas to maintain a suitably lowoxygen level (e.g., purified nitrogen).

The present invention also encompasses ceramic-coated copper substratesprepared by the methods of the present invention (e.g., a PLZT-coatedcopper substrate), as well as devices comprising the ceramic coatedcopper materials (e.g., a capacitor comprising the ceramic-coated coppersubstrate. In some preferred embodiments, the PLZT on the coppersubstrate has a polycrystalline pervoskite phase without observablecopper oxide peaks at 2 θ of 29.2 and 36.2 as determined by X-raydiffraction (XRD) analysis.

Examples

Thin films of Pb_(0.92)La_(0.08)Zr_(0.52)Ti_(0.48)O₃ (PLZT 8/52/48) wereprepared by sol-gel synthesis using lead acetate trihydrate, titaniumisopropoxide, zirconium propoxide, lanthanum nitrate hexahydrate, and2-MOE. A 20 mol % excess of lead was used in the starting solution tocompensate for the lead loss during the high temperaturecrystallization. A detailed procedure for the solution synthesis isreported elsewhere [9]. Copper substrates (0.5 mm thick; 99.8% pure,ESPI Metals) were polished with a 1 μm diamond paste to a RMS surfaceroughness of about 5 nm, and then ultrasonically cleaned in acetone andmethanol prior to coating. The 0.5M PLZT stock solution was spin coatedonto the substrate at about 3000 revolutions-per-minute (rpm) for about30 seconds (sec) and dried in a furnace at about 250° C. in air forabout 10 minutes (min). The film was then pyrolyzed at about 450° C. forabout 18 min under flowing N₂ (99.999%, 500 standard cubic centimetersper minute, sccm) using a heating and cooling rate of about 4° C./min.The applying, drying, and pyrolysis steps were repeated two more times,and then the sample was crystallized at about 650 to 700° C. for about18 min (2° C./min ramp rate) in 500 sccm of flowing N₂ (pO₂ of about10⁻⁶−10⁻⁸ atm). This crystallization step, after 3 layers, is importantto avoid cracks and realize thicker films. The entire process, up to andincluding crystallization, was repeated 1-2 times to yield a thickerfilm. In the case of the single layer sample, the spin, dry, pyrolysisand crystallization was carried out only once. Platinum top electrodes(250 μm diameter and 100 nm thick) were then deposited by electron beamevaporation using a shadow mask. Phase identification was carried outusing x-ray diffraction (Bruker D8 XAS system), while microstructuraland thickness analysis was obtained using a field emission scanningelectron microscopy (FE-SEM; Hitachi S4700). Dielectric measurementswere made with an HP 4192A impedance analyzer using an oscillator levelof 0.1 V at 10 kHz. A Keithley 237 high voltage source meter and RadiantRT600HVAS were used to measure the leakage current (electric field, E,of about 90 kV/mm), and polarization-electric field (P-E) loops.

The major factors that contribute to the oxidation of copper are the pO₂level, temperature, presence or absence of water, and the choice ofsolution chemistry employed. It has been reported that Cu₂O can form attemperatures as low as about 250° C. in air [5], but the temperaturerequired for complete removal of organics (pyrolysis) in the filmstypically is about 300 to about 450° C., depending on the solutionchemistry used. Therefore, in the process of the present invention, eachlayer was first dried at about 250° C. in air and then pyrolyzed atabout 450° C. in flowing N₂ to avoid copper oxidation. FIG. 1 shows theprimary x-ray diffraction (XRD) peaks of one (about 115 nm), three(about 345 nm) and six (about 690 nm) layer PLZT films crystallized atabout 650° C. on copper substrates. Only the major PLZT and Cu₂O peaksare shown, while other peaks are omitted for clarity. A plain polishedcopper substrate was analyzed along with the PLZT samples for thepurpose of comparison.

The XRD patterns of the PLZT films in FIG. 1 indicate that only arandomly oriented polycrystalline perovskite phase was obtained, withoutany copper oxidation. The major Cu₂O peaks (2θ about 29.2 and about36.2) are absent in the PLZT on copper samples, while considerableoxidation occurred in the plain polished copper substrate. Thisobservation was further confirmed upon physical examination of thesamples after crystallization, where the substrates that contained thePLZT films looked reflective to the naked eye, while the surface of theplain polished copper was black due to massive copper oxidation. Whilethe pO₂ level (10⁻⁶−10⁻⁸ atm) in the furnace during crystallization wasthermodynamically conducive to the formation of Cu₂O, a single layer(about 115 nm thick) of PLZT was sufficient to avoid Cu₂O formation.Although this finding suggests the existence of a much lower pO₂ levellocally at the film/substrate interface, similar to that reported byYang et at for the Ni—BaTiO₃ system [10] it is also plausible that asingle layer may physically act as a barrier layer, limiting thediffusion of oxygen to the interface. This also implies that thestrategy of crystallizing a single layer might resolve the crackingissues reported by Losego et al. [6] while still preventing substrateoxidation. The inset of FIG. 1 presents a typical SEM micrograph of thefilms, with average grain size falling between 150 and 200 nm.

FIG. 2 shows the P-E loops of PLZT films crystallized at about 650° C.,675° C., and 700° C. All the films exhibited good ferroelectricbehavior, with the loops gradually becoming wider with increasingtemperature. Films crystallized at 650° C. exhibited slim and wellsaturated loops with P_(r) of about 24 μC/cm², which is comparable tothat of high quality ferroelectric films on Pt/Si [11]. The coercivefield increases by about 75% when the crystallization temperature isincreased above 650° C., suggesting that the film becomes electricallyharder when crystallized at higher temperatures.

FIG. 3 shows the leakage current density (at E of about 90 kV/cm) offilms crystallized at different temperatures. The typical leakagecurrent density (J) was about 3.9×10⁻⁹ A/cm² for films made at 650° C.The leakage current density (at 1000 sec) increased by about 65% whenthe crystallization temperature was increased from 650° C. to about 700°C. It is well known the oxygen vacancy formation in perovskite materialsis accelerated with increasing crystallization time and temperatureunder low pO₂ processing conditions. The typical characteristics ofoxygen vacancy are the creation of two electrons for charge compensationand the ability to inhibit domain wall movement, which increases theelectrical conductivity and the coercive field of ferroelectricmaterials, respectively. Thus, we attributed the observed increase incoercive field and leakage current, with increasing crystallizationtemperature, to an increase in the oxygen vacancy concentration in thefilm. These characteristics are consistent with results reported in theliterature [12].

FIG. 4 shows the dielectric response as a function of bias field forfilms crystallized at 650° C. These films exhibit well definedhysteresis, saturation at high field and a good dielectric tunability. Adielectric constant of about 730, dielectric loss (tan δ)<0.06 anddielectric tunability of about 70% were typically observed for thesefilms. The measured permittivity values are still lower for thiscomposition than that reported (ε of about 1300) for PLZT on LNObuffered nickel substrates [13].

While not wishing to be bound by theory, it is likely that the increasedoxygen vacancy concentration in the film is due to the slow heating andcooling rates (i.e. films were exposed to high temperatures for a longerperiod) employed in the crystallization step was responsible for thedegradation in the electrical properties. This can be avoided by usingrapid thermal annealing (RTA) or the direct insertion technique. Forexample, directly inserting a sample into the furnace at 650° C. for 18min under 500 sccm of flowing N₂ afforded a material with: dielectricconstants >900 and dielectric loss <6%. It should also be noted that theimproved dielectric response may be a result of increased filmdensification due to delayed crystallization caused by the rapid heatingrate [14]. The inset of FIG. 4 represents the temperature coefficient ofcapacitance (TCC) of a PLZT film on Cu of the invention along with thatof commercially manufactured X8R capacitors (shaded region). To thelimits of measurement capability, the TCC for the product of theinvention falls within the tolerance limits of the X8R capacitors. Thedotted line represents extrapolated values.

FIG. 5 shows the relaxation current density measured as a function oftime at room temperature with applied electric field E of about 90 kV/cmon Pt/PLZT/Cu capacitor, along with the fitting of the data to Curie-vonSchweidler equation (solid line). From the curve, a value of n=0.99 andsteady state leakage current density J_(S)=7.3×10⁻⁹ A/cm² were obtained.

FIG. 6 shows the relative permittivity and dielectric loss as a functionof temperature measured on a 1.2-cm×1.2-cm Pt/PLZT/Cu film-on-foilsample. Relative permittivity increases while dielectric loss decreaseswith increasing temperature between room temperature and 175° C. Arelative permittivity of about 1400 and dielectric loss of about 5% weredetermined at 150° C. These results measured on Pt/PLZT/Cu arecomparable to those obtained on Pt/PLZT/LNO/Ni samples.

In summary, 2-MOE based solution synthesis was successfully used to makePLZT thin films on copper substrates, thus adding to the list ofcopper-compatible solution chemistries reported in the literature.Surprisingly, a thin layer (about 115 nm) of PLZT film was sufficient toprotect the underlying copper substrate from oxidation, implying alarger pO₂ processing window than that achievable by thermodynamiccontrol. Device quality PLZT thin films made on copper substratesexhibited the following properties: ε of about 730, tan δ<0.06,J=3.9×10⁻⁹ A/cm² and TCC <15%. The change in capacitance falls with inthe tolerance limits of commercially available X8R capacitors.Electrical measurements suggest that the oxygen vacancies formed due tolow pO₂ processing may be responsible for the degradation in theelectrical properties, and may be accelerated with increasingcrystallization time and temperature. The degradation of the filmquality can be reduced by decreasing the time that the sample is exposedto higher temperatures by use of RTA. Initial results with this approachhave been encouraging with films exhibiting ε>900, tan δ<0.06 and withno copper oxidation.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

REFERENCES

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1. A method for fabricating a ceramic film on a copper substrate, themethod comprising the steps of: (a) applying onto a copper substrate alayer of a sol-gel composition comprising a precursor of a ceramicmaterial in 2-methoxyethanol; (b) drying the layer of step (a) at atemperature up to about 250° C. in air; (c) pyrolyzing the dried layerfrom step (b) at a temperature in the range of about 300 to about 450°C. under a flowing stream of an inert gas to form a ceramic film fromthe ceramic precursor; (d) optionally applying one or two additionallayers of the sol-gel composition onto the ceramic film from step (c)and repeating steps (b), and (c) for each additional layer, to build upa thicker ceramic film on the copper substrate; (e) crystallizing theceramic film at a temperature in the range of about 600 to about 750° C.under a flowing stream of an inert gas; and (f) optionally applying oneor more additional layers of the sol-gel composition onto thecrystallized ceramic film from step (e), and repeating (b), (c), (d),and (e) for each additional layer.
 2. The method of claim 1 wherein theapplying a layer of a sol-gel composition comprises spin coating thesol-gel composition onto the copper substrate.
 3. The method of claim 1wherein the ceramic material is a lead-lanthanum-zirconium-titaniumoxide material and the ceramic precursor comprises a lead compound, alanthanum compound, a zirconium compound and a titanium compound.
 4. Themethod of claim 3 wherein the ceramic precursor comprises a lead salt, atitanium alkoxide, a zirconium alkoxide, and a lanthanium salt.
 5. Themethod of claim 4 wherein the lead salt comprises lead acetate.
 6. Themethod of claim 4 wherein the titanium alkoxide comprises titaniumisopropoxide.
 7. The method of claim 4 wherein the zirconium alkoxidecomprises zirconium propoxide.
 8. The method of claim 4 wherein thelanthanum salt comprises lanthanum nitrate.
 9. The method of claim 1wherein the copper substrate comprises a copper foil having a thicknessin the range of about 0.01 mm to about 1 mm.
 10. The method of claim 9wherein the copper foil has a thickness in the range of about 0.2 toabout 0.5 mm.
 11. The method of claim 1 wherein the copper substrate hasa polished surface with a RMS surface roughness of not more than about10 nm.
 12. The method of claim 1 wherein the drying is performed atabout 250° C.
 13. The method of claim 1 wherein the pyrolyzing isperformed at a temperature of about 450° C.
 14. The method of claim 1wherein the crystallizing is performed at a temperature of about 600 toabout 750° C.
 15. The method of claim 1 wherein the inert gas comprisesnitrogen capable of maintaining pO₂ of less than about 10⁻⁶ atm.
 16. Themethod of claim 1 comprising applying one or two additional layers ofthe sol-gel composition onto the ceramic film from step (c) andrepeating steps (b), and (c) for each additional layer, to build up athicker ceramic film on the copper substrate, prior to crystallizing theceramic film.
 17. The method of claim 16 comprising applying one or moreadditional layers of the sol-gel composition onto the crystallizedceramic film from step (e), and repeating (b), (c), (d), and (e) foreach additional layer.
 18. A method for fabricating alead-lanthanum-zirconium-titanium (PLZT) ceramic film on a coppersubstrate, the method comprising the steps of: (a) applying onto thecopper substrate a layer of a sol-gel composition containing a ceramicprecursor comprising a lead compound, a lanthanum compound, a zirconiumcompound, and a titanium compound in 2-methoxyethanol; (b) drying thelayer of step (a) at a temperature up to about 250° C.; (c) pyrolyzingthe dried layer from step (b) at a temperature in the range of about 300to about 450° C. under a flowing stream of an inert gas to form a PLZTceramic film from the ceramic precursor; (d) optionally applying one ortwo additional layers of the sol-gel composition onto the ceramic filmfrom step (c) and repeating steps (b), and (c) for each additionallayer, to build up a thicker ceramic film on the copper substrate; (e)crystallizing the ceramic film from step (c) at a temperature in therange of about 600 to about 750° C. under a flowing stream of an inertgas; and (f) optionally applying one or more additional layers of thesol-gel composition onto the crystallized ceramic film from step (e),and repeating (b), (c), (d), and (e) for each additional layer.
 19. Themethod of claim 18 wherein the pyrolyzing is performed at a temperatureof about 450° C.
 20. The method of claim 18 wherein the crystallizing isperformed at a temperature of about 600 to about 750° C.
 21. Aceramic-coated copper substrate prepared by the method of claim
 1. 22. APLZT-coated copper substrate prepared by the method of claim
 18. 23. Acapacitor comprising the ceramic-coated copper substrate of claim 21.24. A capacitor comprising the PLZT-coated copper substrate of claim 22.25. The PLZT-coated copper substrate of claim 22 wherein the PLZT has apolycrystalline pervoskite phase without observable copper oxide peaksat 20 of 29.2 and 36.2 as determined by X-ray diffraction (XRD)analysis.